Test CDL Combination Vehicles

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1. 1. Which pair of habits does the most to keep a loaded combination vehicle from rolling over?

   • A. Load the heaviest cargo on top and brake hard just before each curve
   • B. Push the load toward one side wall so it cannot shift, and keep your speed up through ramps
   • C. Keep the cargo as close to the ground as possible, and drive slowly around turns
   • D. Run the trailer a little overloaded so it settles lower on its springs
   Mostra risposta e spiegazione

   Risposta: C. Keep the cargo as close to the ground as possible, and drive slowly around turns

   Stacking cargo high raises the center of gravity, and a higher center of gravity tips more easily, which is why a fully loaded rig is far more likely to roll in a crash than an empty one. Keeping the load low and slowing down for corners, ramps and off ramps are the two things a driver controls directly. Centering the load matters too, because a load pushed to one side makes the trailer lean and starts the roll for you.

2. 2. You are making a tight right turn and cannot finish it without using part of the next lane. What does off-tracking tell you to do?

   • A. Swing wide to the left before you start the turn, so the trailer has room
   • B. Start the turn close to the curb and swing wide as you complete it, keeping the rear near the curb
   • C. Turn from the left lane every time, because the trailer wheels track outside the tractor wheels
   • D. Nothing, since off-tracking only affects backing
   Mostra risposta e spiegazione

   Risposta: B. Start the turn close to the curb and swing wide as you complete it, keeping the rear near the curb

   Going around a corner, the rear wheels follow a tighter path than the front wheels, and the rear wheels of the trailer cut in the most. So you have to steer the front end wide enough that the rear does not climb the curb. Swinging left first invites a following driver to think you are turning left and slip up your right side, which is where your trailer is about to be. Turning wide at the end instead, with the rear kept close to the curb, blocks that gap.

3. 3. Rearward amplification, the crack the whip effect, is greatest in which of these?

   • A. A bobtail tractor with no trailer
   • B. A three axle tractor pulling one short semitrailer
   • C. A five axle tractor semitrailer with a 45 foot trailer
   • D. The last trailer of a set of triples
   Mostra risposta e spiegazione

   Risposta: D. The last trailer of a set of triples

   In a quick lane change, each trailer swings harder than the unit ahead of it, so the more trailers you add, the more the back one whips. The CDL manual charts this: a five axle tractor semitrailer sits near the bottom of the scale and triples sit at the top, roughly three and a half times as easy to roll at the last trailer. That is why you steer gently and smoothly, look far enough ahead to avoid sudden lane changes, and slow down before a turn rather than during it.

4. 4. You brake hard on a wet ramp and see in your mirror that the trailer is starting to swing out. What is the first thing you do?

   • A. Release the brakes so the trailer wheels can roll and get traction back
   • B. Press the brake pedal harder to pull the trailer back in line
   • C. Apply the trailer hand valve to straighten the rig out
   • D. Set the parking brake and steer toward the shoulder
   Mostra risposta e spiegazione

   Risposta: A. Release the brakes so the trailer wheels can roll and get traction back

   A trailer jackknife starts when the trailer wheels lock up and slide, which happens most easily when the trailer is empty or lightly loaded. Locked wheels cannot steer or track, so the fix is to stop braking and let them roll again. Once they grip, the trailer follows the tractor and straightens itself out. Checking your mirrors every time you brake hard is what buys you the time to catch it, because once the trailer leaves your lane it is very hard to save.

5. 5. What is the trailer hand valve, also called the trolley valve or Johnson bar, actually for?

   • A. Holding the rig on a grade instead of using the parking brakes
   • B. Straightening the rig out when the trailer begins to swing
   • C. Testing the trailer brakes, and nothing else
   • D. Releasing the trailer spring brakes before you pull away
   Mostra risposta e spiegazione

   Risposta: C. Testing the trailer brakes, and nothing else

   The hand valve applies the trailer brakes only, which is exactly the condition that starts a trailer skid, so it has no place in normal driving. The foot brake sends air to every brake on the rig, tractor and trailer together, and is far less likely to jackknife you. It is also wrong for parking, because on a trailer without spring brakes the air can leak away overnight and release the brakes, so use the parking brakes and chock the wheels.

6. 6. You crawl under with a flashlight after coupling and see a gap between the upper and lower fifth wheel. What does that mean?

   • A. The coupling is wrong, and the kingpin may be sitting on top of the closed jaws
   • B. It is normal, because the plate needs clearance for grease
   • C. The trailer is loaded too heavy and is lifting the plate slightly
   • D. Nothing, as long as the tug test already passed
   Mostra risposta e spiegazione

   Risposta: A. The coupling is wrong, and the kingpin may be sitting on top of the closed jaws

   There should be no visible space at all between the upper and lower fifth wheel. A gap usually means the jaws closed before the kingpin dropped in, so the pin is resting on top of them instead of being captured, and the trailer can come loose very easily. This is one of the reasons you shut the engine off, take the key with you and look with a light rather than trusting the tug test alone. If the coupling is not right, do not drive it, get it fixed.

7. 7. When you look into the back of the fifth wheel, the locking jaws should be closed around which part of the kingpin?

   • A. The head
   • B. The shank
   • C. The base plate
   • D. The trailer apron
   Mostra risposta e spiegazione

   Risposta: B. The shank

   The kingpin has a base, a narrower shank and a wider head at the bottom. The jaws are meant to wrap the shank, so the head sits below them and cannot pull up through. Jaws closed around the head look locked from a distance but hold almost nothing. While you are under there, also confirm the locking lever is in the lock position and the safety latch is seated over it, since on some fifth wheels that catch has to be placed by hand.

8. 8. You couple to a modern trailer with spring brakes and accidentally cross the air lines. What happens?

   • A. The trailer brakes drag but the rig still rolls normally
   • B. Nothing changes, because both lines carry the same air
   • C. The marker lights fail while the brakes keep working
   • D. Supply air goes to the service line, the trailer tanks never charge, and the spring brakes will not release
   Mostra risposta e spiegazione

   Risposta: D. Supply air goes to the service line, the trailer tanks never charge, and the spring brakes will not release

   Air meant to fill the trailer tanks gets sent down the service line instead, so there is never enough pressure to push the spring brakes off. If you push the trailer air supply control and the spring brakes stay set, check your glad hand connections first. The dangerous version is an older trailer with no spring brakes and a drained tank: crossed lines there let you drive away with no trailer brakes at all, which is why you shut the engine off and listen for the trailer brakes applying and releasing before you move.

9. 9. A trailer breaks away and tears the emergency line apart. What happens next?

   • A. The tractor loses its air too, and the driver is left with no brakes
   • B. The tractor protection valve closes to keep air in the tractor, and the trailer emergency brakes come on
   • C. Only the trailer lights go out, because the emergency line is electrical
   • D. The service line keeps the trailer brakes released until the trailer tank drains
   Mostra risposta e spiegazione

   Risposta: B. The tractor protection valve closes to keep air in the tractor, and the trailer emergency brakes come on

   The emergency line does two jobs: it charges the trailer air tanks and it holds the trailer emergency brakes off. Lose pressure in it and those brakes apply on their own. At the tractor end, the tractor protection valve shuts so the tractor keeps the air it needs for its own brakes, and the red eight sided trailer air supply knob pops out. That valve closes by itself once pressure falls into the range the manufacturer specifies, usually somewhere between 20 and 45 psi.

10. 10. Before you back the tractor under the trailer, which of these must already be done?

    Seleziona tutte le risposte corrette.

    • A. The trailer wheels are chocked, or the trailer spring brakes are set
    • B. The tractor is lined up directly in front of the trailer, not at an angle
    • C. The trailer is set low enough that the tractor lifts it slightly as it backs under
    • D. The landing gear is fully raised and the crank handle is secured
    • E. The electrical cord is plugged into the trailer and the safety catch is fastened
    Mostra risposta e spiegazione

    Risposta: A. The trailer wheels are chocked, or the trailer spring brakes are set, B. The tractor is lined up directly in front of the trailer, not at an angle, C. The trailer is set low enough that the tractor lifts it slightly as it backs under

    Chocking or setting the trailer brakes keeps the trailer from walking away as the tractor pushes into it. Backing under at an angle can shove the trailer sideways and snap the landing gear, so line up straight and check both sides in your mirrors. Trailer height matters in both directions: too low and you hit the trailer nose, too high and the pin will not seat. The electrical cord goes on after you have crawled under and inspected the coupling, and the landing gear comes up last of all.

11. 11. Which walkaround checks are added because the vehicle is a combination, and are not part of a straight truck inspection?

    Seleziona tutte le risposte corrette.

    • A. The lower fifth wheel is mounted securely, greased, with no visible space against the upper plate
    • B. The air and electrical lines are connected, undamaged, and secured with enough slack for turns
    • C. The landing gear is fully raised and undamaged, with the crank handle in place and secured
    • D. The windshield wipers are secure and the blades are not torn
    • E. The steering wheel has no more than the allowed amount of free play
    Mostra risposta e spiegazione

    Risposta: A. The lower fifth wheel is mounted securely, greased, with no visible space against the upper plate, B. The air and electrical lines are connected, undamaged, and secured with enough slack for turns, C. The landing gear is fully raised and undamaged, with the crank handle in place and secured

    You still run the same seven step inspection, plus a set of items that only exist once there is a trailer behind you: the coupling system, the lines that cross to the trailer, and the landing gear. On a sliding fifth wheel you also confirm every locking pin is present and locked, and that the fifth wheel is not so far forward that the tractor frame will strike the landing gear in a sharp turn. Wipers and steering play belong to the ordinary inspection you already do on any vehicle.

12. 12. You are dropping a loaded trailer. Which of these are the correct actions?

    Seleziona tutte le risposte corrette.

    • A. Shut off the trailer air supply to lock the trailer brakes, back up gently against the kingpin, then set the parking brake while the tractor is still pushing
    • B. After the landing gear makes firm contact with the ground, crank a few extra turns in low gear to take some weight off the fifth wheel
    • C. Pull forward only until the fifth wheel clears, leaving the tractor frame under the trailer, then get out and check the supports
    • D. Pull the release handle and drive straight out in one move, since the landing gear will catch the trailer
    • E. Leave the air lines connected so the trailer keeps its brakes applied after you drive away
    Mostra risposta e spiegazione

    Risposta: A. Shut off the trailer air supply to lock the trailer brakes, back up gently against the kingpin, then set the parking brake while the tractor is still pushing, B. After the landing gear makes firm contact with the ground, crank a few extra turns in low gear to take some weight off the fifth wheel, C. Pull forward only until the fifth wheel clears, leaving the tractor frame under the trailer, then get out and check the supports

    Backing gently against the kingpin takes the load off the locking jaws so the release handle will move, and setting the parking brake holds it there. On a loaded trailer, a few extra cranks lift a little weight off the fifth wheel, which makes the jaws easier to open now and easier to couple next time, though you never lift the trailer off the plate. Stopping with the tractor frame still under the trailer means that if the landing gear sinks or collapses, the trailer lands on your frame instead of the ground.

13. 13. Complete the sentence.

    On a rig pulling more than one trailer, the shut-off valves in the service and supply lines must be _____ at the rear of the last trailer and _____ on all the others.

    Opzioni per lo spazio 1: open, closed, removed

    Opzioni per lo spazio 2: open, closed, capped

    Mostra risposta e spiegazione

    Risposta: closed, open

    Those valves exist so the lines can be sealed off when nothing is being towed behind that trailer. Leave the last one open and air escapes out the back, so nothing downstream of the leak builds pressure. Leave a middle one closed and the trailers behind it never get air at all. You check this by opening the valve at the rear of the last trailer and listening for air, which proves the whole system is charged all the way back.

14. 14. Complete the sentence.

    To check that the coupling caught, raise the landing gear slightly off the ground, keep the trailer brakes locked, and _____.

    Opzioni per lo spazio 1: pull the tractor gently forward, rock the tractor back and forth in reverse, release the parking brake and let the rig roll backward, apply full throttle against the trailer

    Mostra risposta e spiegazione

    Risposta: pull the tractor gently forward

    A gentle tug against locked trailer brakes is the quickest proof that the jaws actually captured the kingpin rather than sliding past it. Keep it gentle, because a hard pull against a bad coupling is how a trailer ends up on the ground. Passing the tug is not the end of it either. You still put the transmission in neutral, set the parking brakes, shut the engine off, take the key with you and inspect the coupling by eye before anything else.

15. 15. Complete the sentence.

    The service line, which carries the air your foot brake meters out to the trailer, is usually color coded _____, while the emergency line, which fills the trailer air tanks and holds the emergency brakes off, is usually color coded _____.

    Opzioni per lo spazio 1: blue, red, green, yellow

    Opzioni per lo spazio 2: blue, red, black

    Mostra risposta e spiegazione

    Risposta: blue, red

    The service line is also called the control line or signal line, and the pressure in it rises and falls with how hard you press the pedal, which is what tells the relay valves how much brake to apply. The emergency line is also called the supply line, and it does the two jobs above at once. Colors are a helpful habit and not a guarantee, so read the metal tags stamped service and emergency when they are fitted, and clean the rubber seals before you couple the glad hands.

Cosa copre davvero il test combination vehicles

Il test combination vehicles è uno dei test teorici che fai all'ufficio patenti del tuo stato, e lo sostiene ogni candidato Class A. È separato dal test general knowledge, separato dal test air brakes e separato dall'abilitazione doubles and triples, quindi la maggior parte dei candidati Class A finisce per fare almeno tre test scritti prima ancora di toccare un camion. Gli stati scrivono i propri set di domande dallo stesso modello di manuale CDL, quindi il numero di domande, il tempo, la tariffa e quanto presto puoi ripetere dopo una bocciatura cambiano da stato a stato. La soglia di superamento non cambia allo stesso modo. Le norme federali richiedono che tu risponda correttamente ad almeno l'80 per cento delle domande di ogni test teorico, quindi uno stato che te ne dà 20 ti lascia sbagliarne quattro, e uno che te ne dà 50 ti lascia sbagliarne dieci.

I contenuti vengono dalla Sezione 6 del manuale CDL del tuo stato, e si dividono in cinque parti. Guidare in sicurezza i veicoli combinati copre il rischio di ribaltamento e il baricentro, sterzare dolcemente e l'effetto colpo di frusta, frenare in anticipo, i rimorchi bassi che si incastrano sui passaggi a livello rialzati, le sbandate del rimorchio, le svolte larghe per via dell'off-tracking, cioè le ruote posteriori che tagliano la curva, e la retromarcia con il rimorchio. I freni ad aria dei veicoli combinati coprono la trailer hand valve, il comando a mano del freno rimorchio, la tractor protection valve, che protegge l'aria della motrice, il comando dell'alimentazione aria del rimorchio, il tubo di servizio e quello di emergenza, le glad hand, i raccordi rapidi che collegano i tubi dell'aria, i serbatoi aria del rimorchio e i rubinetti di intercettazione. I freni antibloccaggio hanno una breve parte tutta loro, in gran parte su ciò che l'ABS non fa per te. Poi arrivano i passaggi numerati di aggancio e sgancio, e le voci in più che si aggiungono al giro di ispezione quando hai un rimorchio dietro.

I passaggi di aggancio e sgancio meritano la fetta più grande del tuo tempo di studio, perché escono due volte. Vengono chiesti in questo test scritto, e più avanti devi trovare, toccare e nominare ad alta voce le parti dell'aggancio durante la parte pre-viaggio della prova pratica. Altre due cose vanno sistemate presto. Scarica il manuale del tuo stato invece di un PDF generico, perché il tuo stato scrive le domande dalla versione che pubblica e la formulazione coinciderà. E controlla a che punto sei con l'entry level driver training. Da febbraio 2022 le norme federali richiedono la formazione presso un ente iscritto al registro federale prima di poter sostenere la prova pratica per una prima patente Class A, ed è un passaggio separato da tutti i test teorici.

Come usare questo assaggio e come studiare la Sezione 6

Queste 15 domande puntano sul ragionamento dietro le regole più che sul lessico. Chiedono perché il rimorchio si ribalta prima della motrice, perché in una sbandata del rimorchio rilasci il freno invece di aggiungerne, cosa succede davvero quando le glad hand vengono incrociate, e in che ordine vanno i passaggi di aggancio. È la parte che il test scritto premia, ed è anche la parte che ti tiene in piedi su una rampa bagnata di notte. Le domande mescolano i formati che usa un test teorico, comprese la risposta multipla e il completamento di frasi, perché scegliere tre risposte giuste su cinque è un controllo più duro e più onesto di quello che sai rispetto a sceglierne una su quattro.

Fallo tutto d'un fiato senza appunti, poi leggi la spiegazione di ogni domanda, comprese quelle che hai azzeccato. Tratta una risposta sbagliata come un argomento, non come un singolo dato. Se hai sbagliato la domanda sui tubi dell'aria incrociati e quella sulla tractor protection valve, torna a rivedere tutta la sottosezione sui tubi dell'aria in blocco, perché il tubo di servizio e quello di emergenza hanno senso solo come coppia. Lo stesso vale per il ribaltamento e l'amplificazione posteriore, che sono due viste dello stesso problema, visto che un carico alto e un rimorchio che frusta finiscono entrambi con il cassone su un fianco. Qui niente viene valutato o salvato da nessuna parte, quindi non ti costa nulla farlo a freddo e scoprire cosa non sai ancora.

Per i passaggi di aggancio leggere non basta. Scrivi a memoria i sedici passaggi di aggancio e i dieci di sgancio, in ordine, finché non ci riesci senza guardare, poi dilli ad alta voce mentre giri intorno a un mezzo vero se ne hai la possibilità. L'ordine porta con sé la logica di sicurezza, e la logica è ciò che fa restare in testa l'ordine. Metti i cunei alle ruote prima di posizionare la motrice, blocchi i freni del rimorchio prima di infilarti sotto, ti infili sotto con una torcia e controlli le ganasce prima di collegare il cavo elettrico, e alzi i piedini di appoggio per ultimi. Azzecca l'ordine e buona parte delle singole domande si risponde da sola.

Come StudyPDF crea test completi dal tuo materiale CDL

Quindici domande ti mostrano dove traballi. Da sole non bastano per arrivare pronto, e una banca dati generica si allontana dalla formulazione usata dal manuale del tuo stato, che è la formulazione da cui è scritto il tuo test. Una volta che conosci le tue aree deboli, quello che ti serve dopo è volume su quelle aree precise, tratto dalle pagine che ti hanno davvero dato.

StudyPDF prende un'altra strada. Carichi il manuale CDL del tuo stato, la dispensa sulla Sezione 6 della tua scuola o gli appunti che ti ha dato l'istruttore, e Bo, l'agente di studio, crea test completi da quelle pagine esatte. Ogni domanda nasce dal tuo materiale e ogni spiegazione indica da dove viene la risposta, così puoi andare dritto alla fonte quando qualcosa non ti torna. Puoi generare test nuovi quante volte vuoi, restringerli a un'area sola come l'aggancio e lo sgancio o i tubi dell'aria, e tenere traccia degli argomenti che continui a sbagliare.

Per iniziare non devi caricare niente. Se non hai un file sotto mano, nomina invece un argomento, per esempio l'aggancio di una motrice con semirimorchio, la tractor protection valve o come evitare le sbandate del rimorchio, e Bo ci scrive sopra un test. Aiuta quando stai aspettando il fascicolo della scuola, o studi da un manuale che hai solo su carta. Inizi gratis.